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Hot Structures:

July 31, 2006

Dryden's Flight Loads Laboratory is one of the only government
facilities available for researching mechanical and thermal loads
simultaneously on everything from large structures or systems up to
full-sized aircraft.

"There are only a few places in the U.S. that can do this type of
large-scale testing within the government and we're the only one on
the West Coast," said Larry Hudson, loads lab thermal structures test
engineer.

This unique capability may soon be put to use testing the latest
components and subsystems for hypersonic and space-faring vehicles,
Hudson said.

One application for the loads lab research can be seen in recently
completed work on the X-37 prototype, a reusable space vehicle being
developed by the government. Once a NASA project (managed at
Marshall Space Flight Center, Huntsville, Ala.), the Dryden lab
completed thermal and mechanical testing on three key X-37 components
when the program transitioned to management by the Defense Advanced
Research Projects Agency, or DARPA. Also researched at Dryden was a
fourth test article considered critical to future space vehicles with
a design similar to that of the X-37.

Key partners in the testing effort included The Boeing Company,
Huntington Beach, Calif.; Science Applications International Corp.,
San Diego; Carbon-Carbon Advanced Technologies, Fort Worth, Texas;
General Electric Energy, Newark, Del.; Materials Research and Design,
Wayne, Pa., and the Air Force Research Laboratory at Wright-Patterson
Air Force Base, Ohio.

Research on the three X-37 components involved more than 30 tests
during a two-year period from 2003 to 2005. Components were heated to
more than 2,500 degrees Fahrenheit. The components tested included a
carbon silicon carbide flaperon subcomponent, a carbon-carbon
flaperon subcomponent and a carbon-carbon flaperon qualification unit.
The flaperon accounts for two of the X-37's five flight control
surfaces. It is used for roll control and to adjust for drag during
atmospheric flight and airspeed during approach and landing. The
flaperons are located on the trailing edge of each wing.

For the X-37 flaperon qualification unit, test objectives included
verifying the structural model and finite element analysis, or FEA,
used to design the carbon-carbon flaperon; verifying the thermal
analysis model used to predict temperature distributions and time
histories in the flight environment; demonstrating the
manufacturability of the flaperon design and evaluating the
structural performance of design elements under representative
flight, thermal and static load conditions, and verifying the
mechanical and thermal properties of carbon-carbon materials used in
the design analysis.

The thermal and mechanical loading conditions applied to the
components simulated what the parts would encounter in actual flight.
The tests qualified the flaperon design and manufacturing methods for
flight, and information from the tests will be used in evaluating
thermal and loading models associated with creating parts for
hypersonic and space vehicles.

About 15 to 20 people, including customer staff members, conducted
the research. Loads lab staff designed, fabricated and assembled
unique equipment used to perform the tests. So successful was the
team that it was recognized at Dryden with a 2005 NASA Group
Achievement Award.

In addition to that work, Hudson said the loads lab also tested a
Next-Generation Launch Technology program item designed as a body
flap envisioned for use in future, X-37-like space-faring vehicles.
Heating and mechanical loading of that test article were not part of
baseline X-37 tests, but the applied thermal and mechanical loads
were derived from X-37-like re-entry trajectory information.

"The Flight Loads Laboratory has the unique ability to perform
large-scale, thermal structure testing ranging from cryogenic
temperatures to temperatures up to the 3,000-degrees-Fahrenheit
range. We also have the ability to define thermal and mechanical
loading on structures. We can do our testing in the air or in an
inert atmosphere (artificially created in the lab setting)," Hudson
said.

"We have unique skills in the area of high-temperature
instrumentation - specifically, the application of high-temperature
fiber optic strain sensors and thermocouple temperature measurements
on advanced materials, such as carbon-carbon and carbon
silicon-carbide."

Technology researched in the loads lab could be used for developing
new capabilities for re-entry vehicles and hypersonic atmospheric
vehicles, Hudson said. High-temperature instrumentation on
carbon-carbon and carbon silicon-carbide structures is a unique
discipline that provides analysts and designers with valuable strain
and temperature data, which aids them in validating analysis and
models.

Hudson sees the information gathered from X-37 research and lessons
learned from that and other loads labs projects as a database that
can be available for hypersonic research within NASA's Aeronautics
program. Using that information to advance technologies required for
development of next-generation hypersonic vehicles is where the loads
lab could potentially make the greatest contribution.

"Our goal," said Hudson, "is to provide accurate data under simulated
flight conditions to analysts so they'll have the best possible
opportunity for validating their models of advanced hot-structures
and thermal protection materials.

"As a follow-on goal, we want to take the validated high-fidelity
models and come up with the tool or tools that can be used to
simplify the model so that it can run faster, yet contain all of the
pertinent information necessary for vehicle designers to do their job
more accurately and efficiently."

In addition to providing information for physics-based modeling
design and analysis and optimization tools, Hudson sees a practical
role for the lab in helping companies advance aeronautics data. For
example, a company needing to qualify a part, subsystem or even an
entire aircraft for use at temperatures up to 3,000 degrees
Fahrenheit could tap loads lab personnel to conduct the necessary
tests.

"Our plan is to partner with private industry and other government
entities through cost-sharing agreements in an effort to advance
structural technologies that are useful to not only our customers,
but also to NASA and the technical community," he said.

Key Dryden Aerostructure Branch Capabilities

Structural, thermal and dynamic analysis

Finite element analysis

Aerodynamic loads analysis

Flutter analysis

Aeroservoelastic analysis

Aeroheating/heat transfer analysis

Structural, thermal and dynamic groundtest techniques

Structural loads calibration and equation derivation

Thermal/structural testing

Proof loads testing

Ground vibration and structural mode interaction testing

Advanced structural instrumentation

Strain, temperature, heat flux, deflection

Fiberoptic strain and temperature sensors

Flight test techniques for analysis validation and safety-offlight support